Chain saw torque limiting centrifugal clutch assembly

ABSTRACT

Disclosed herein is a chain saw including a centrifugal clutch assembly driven by a shaft rotated by an engine supported by a frame, and including a sprocket driver supported for rotation independently of and co-axially with the shaft, a clutch drum supported for rotation independently of and co-axially with the shaft and for releasable driving connection with the shaft in response to shaft rotation above a predetermined speed, together with cooperating surfaces extending radially on each of the sprocket driver and the drum in facing relation to each other, and means for holding the drum and driver surfaces in frictional engagement with each other for torque transmission therebetween below a predetermined torque level, a chain sprocket mounted for rotation co-axially with said shaft and driven by the sprocket driver, a cutter bar supported by the frame, and a saw chain trained around the sprocket and the cutter bar.

United States Patent Arff CHAIN SAW TORQUE LIMITING CENTRIFUGAL CLUTCH ASSEMBLY [75] Inventor: Uwe F. Arff, Peterborough, Ontario,

Canada [73] Assignee: Outboard Marine Corporation,

Waukegan, Ill.

[22] Filed: Aug. 10, 1973 [21] Appl. N0.: 387,340

[52] U.S. Cl 30/383, 192/483, 74/243 CS [51] Int. Cl B27b 17/10 [58] Field of Search 30/381389; 192/483; 64/30 R, 30 LB; 74/243 CS [56] References Cited UNITED STATES PATENTS 2,675,835 4/1954 Kiekhaefer 30/383 3,144,890 8/1964 lrgens.... 30/383 3,192,740 7/1965 Stamates 64/30 R 3,265,172 8/1966 Kunio Atsumi et al 192/55 3,283,863 11/1966 Scheutzow 192/483 X 31,498,346 3/1970 Gasner et al 30/381 Primary Examiner-Al Lawrence Smith Assistant ExaminerK. J. Ramsey Attorney, Agent, or Firm-Michael, Best & Friedrich [5 7 ABSTRACT Disclosed herein is a chain saw including a centrifugal clutch assembly driven by a shaft rotated by an engine supported by a frame, and including a sprocket driver supported for rotation independently of and co-axially with the shaft, a clutch drum supported for rotation independently of and co-axially with the shaft and for releasable driving connection with the shaft in response to shaft rotation above a predetermined speed, together with cooperating surfaces extending radially on each of the sprocket driver and the drum in facing relation to each other, and means for holding the drum and driver surfaces in frictional engagement witheach other for torque transmission therebetween below a predetermined torque level, a chain sprocket mounted for rotation co-axially with said shaft and driven by the sprocket driver, a cutter bar supported by the frame, and a saw chain trained around the sprocket and the cutter bar.

13 Claims, 7 Drawing Figures CHAIN SAW TORQUE LIMITING CENTRIFUGAL CLUTCH ASSEMBLY BACKGROUND OF THE INVENTION The invention relates generally to chain saws and more particularly, to centrifugal clutches for chain saws. Such centrifugal clutches operate in response to rotation above a predetermined speed to drivingly connect a chain carrying drive sprocket to the engine and, in general, allow little, if any slippage in the event the saw chain becomes squeezed in the kerf or otherwise is restrained from movement. Such restraint commonly involves force transmission in excess of the force transmitted from the engine to the chain and can result in damage to the chain, or to the engine, or to intervening components. Such forces can develop so rapidly that conventional centrifugal clutches often cannot react or disengage quickly enough to avoid damge to the chain saw.

Examples of prior chain saw centrifugal clutch constructions are found in the following US. patents:

lrgens 3,144,890 issued August 18, 1964 Deelman 3,339,596 issued September 5, I967 Linkfield 3,519,037 issued July 7, 1970 SUMMARY OF THE INVENTION The invention provides a chain saw with a centrifugal clutch assembly including therein slip clutch means for limiting torque transmission between the driving shaft and the chain sprocket.

More particularly in accordance with the invention, the centrifugal clutch assembly includes a chain sprocket driver supported for rotation independently of and coaxially with the driving shaft, a chain sprocket connected to the sprocket driver for common rotation therewith, a clutch drum supported for rotation independently of and co-axially with the driving shaft and for releasable driving connection with the driving shaft in response to shaft rotation above a predetermined speed, together with cooperating surfaces extending radially on each of the sprocket driver and the drum in facing relation to each other, and means for holding the driver and drum surfaces in frictional engagement with each other for torque transmission therebetween below a predetermined torque level.

Still more specifically, the holding means comprises one or more spring washers reacting between the clutch drum and the sprocket driver to hold the clutch drum and sprocket driver in frictional engagement.

One of the principal features of the invention is the provision of a chain saw including a centrifugal clutch incorporating slip clutch means.

Another of the principal features of the invention is the provision of a chain saw including slip clutch means for limiting torque transmission in the event that the saw chain encounters an obstruction causing an over load condition. Still another of the principal features of the invention is the provision of a chain saw centrifugal clutch assembly which will provide reliable service over a long and useful life and which is economical to manufacture.

Othe features and advantages of the invention will become known by reference to the following drawings, general description and claims.

DRAWINGS FIG. 1 is a perspective view of a chain saw in accordance with the invention.

FIG. 2 is a side elevational view of a centrifugal clutch assembly incorporated in the chain saw shown in FIG. ll.

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2. 7

FIG. 4 is a view similar to FIG. 3 showing the components in their relative positions prior to full assembly.

FIG. 5 is a view similar to FIG. 3 showing a modified chain saw centrifugal clutch assembly in accordance with the invention.

FIG. 6 is a view similar to FIG. 5 showing the components in their relative positions prior to full assembly.

FIG. 7 is a view similar to FIG. 3 showing another modified chain saw centrifugal clutch assembly in accordance with the invention.

Before explaining the'invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purposes of description and should not be regarded as limiting.

GENERAL DESCRIPTION Shown in the drawings is a chain saw 11 including a frame .13 which supports an engine 15 and a cutter bar 17. The engine 15 includes an output shaft 19 which supports and drives a centrifugal clutch 21. In turn, the centrifugal clutch 21 drives a chain sprocket 23 driving a saw chain 25 around the cutter bar 17. If desired, the centrifugal clutch 21 can be supported by and driven by another shaft driven by the engine output shaft 19. As thus far described, the construction is conventional.

As is also conventional, the centrifugal clutch 21 includes (see FIGS. 2 and 3) a clutch drum 31 which is suitably mounted for rotation relative to the shaft 19 and which includes an inner cylindrical surface 33, together with a clutch driver (not shown) which is keyed or otherwise fixed to the shaft 19 for common rotation therewith and one or more clutch shoes (not shown) which are rotated by the driver and carried for movement in response to rotation above a predetermined speed, into driving engagement with the inner cylindris cal surface 33 of the clutch drum 21. i

In accordance with the invention, the centrifugal clutch 21 is a part of a centrifugal clutch assembly 41 which includes slip clutch means 43 provided between the chain sprocket 23 and the clutch drum 31 in order to afford unlimited rotary slippage between the clutch drum 31 and the chain sprocket 23 so as thereby to limit torque transmission therebetween under over load conditions and particularly to limit torque transmission from the chain sprocket 23 through the centrifugal clutch 21 to the engine 15.

Still more particularly, the centrifugal clutch assembly 41 incorporated in the chain saw shown in FIG. 1 is shown in FIGS. 2 and 3 and comprises a sprocket 7 driver 45 including a hub 47 which is rotatably supported on the shaft 19. Also .forming a part of the sprocket driver 45 is a flange 49 which extends from the hub 47 and which includes a shoulder formed by an annular, radially extending surface 51 and a cylindrical surface 53. Adjacent to the cylindrical surface 53, the hub 47 includes an annular groove 55. Axially adjacent to the groove 55, the hub 47 includes a spline portion 57 adapted to receive the chain sprocket 23 so as to rotate the chain sprocket 23 in response to rotation of the sprocket driver 45. Any suitable means, such as a snap ring, (not shown), can be employed to retain the chain sprocket 23 on the sprocket driver 45. Other arrangements for mounting a sprocket and for driving the sprocket from the driver are within the scope of the invention.

In still further accordance with the invention, the clutch drum 31 includes an annular portion 61 with a central aperture 63 and a margin extending around the aperture 63 in the form of a radially extending annular surface65 adapted to engage the annular surface 51 of the sprocket driver 45 so as to transmit torque therebetween. The annular portion 61 also includes a surface 67 spaced axially from the surface.

Also in accordance with the invention, means are provided for holding the clutch drum surface 65 in engagement with the sprocket driver surface 51 so as to facilitate torque transmission therebetween. While various other constructions can be employed, in the construction illustrated in FIGS. 2 through 4, such holding means comprises resilient or spring means in the form of an annular spring washer 71 which reacts between the clutch drum surface 67 and the sprocket driver 45. Various means can be provided to facilitate reaction of the spring washer 71 against the sprocket driver 45. For instance, a snap ring could be seated in the annular groove so as to react against the spring washer 71. In the illustrated construction, the spline portion 57 on the sprocket driver 45 includes a plurality of ribs 73 and the spring washer 71 is provided with a like plurality of spaced notches 75 affording axial movement of the spring washer 71 axially of the splined portion 57. Also provided in the spring washer 71 are a like plurality of recesses or pockets 77 which are located between the notches 75 and which are adapted to receive the axially inner ends of the ribs 73 of the spline portion 57 to prevent axial outward movement of the spring washer 71 relative to the sprocket driver 45. Thus, in assembly, the spring washer 71 is slipped over the splined portion 57 and collapsed until essentially flat, or close to being flat, and then rotated slightly within the groove 55 so as to enable the ends of the spline ribs 73 to seat in the recesses 77 when the force compressing or collapsing the spring is removed.

Spring means other than the washer 71 can also be employed, as for instance, coil spring means or a rubber spring means.

Prior to final assembly, the components of the centrifugal clutch assembly 41 have the relationship shown in FIG. 4, while the final assembly relationship is shown in FIG. 3.

In operation of the centrifugal clutch assembly 41, the force applied by the spring washer 71 holds the surfaces 55 and 65 against each other to permit full torque transmission from the engine to the saw chain 25 without material slippage. However, in the event the saw chain 25 becomes lodged in wood or otherwise encounters an obstacle, the slip clutch means 43 incorporated in the centrifugal clutch assembly 41 will prevent imposition of excessive strain on both the saw chain 25 and the engine 15 by permitting slippage as soon as an over load condition develops.

Shown in FIGS. 5 and 6 is another chain saw centrifugal clutch assembly 101 which is in accordance with the invention and which is constructed in essentially the same manner as is the centrifugal clutch assembly 41, except as described below. Accordingly, the same reference numerals have been applied to components shown in FIGS. 5 and 6 as have been applied to the corresponding components of the construction shown in FIGS. 2 through 4.

The centrifugal clutch assembly 101 differs from the centrifugal clutch assembly 41 by reason of the incorporation ofa backing washer 103 which, in effect, constitutes another spring washer, which is oppositely arranged with respect to the spring washer 71, and which preferably includes an annular outer lip or flange 105. Prior to final assembly, the two spring washers 71 and 103 have the relationship shown in FIG. 6, while the final assembly relationship is shown in FIG. 5.

The construction shown in FIG. 5 affords the advantage of applying axial force from the spring backing washer 103 to the clutch drum 31 over a larger area then is the case with the essentially linear engagement between the spring washer 71 and the clutch drum 31 as shown in the construction illustrated in FIGS. 2 through 4.

Shown in FIG. 7 is still another centrifugal clutch assembly 125 which is essentially of the same construction as that shown in FIGS. 2 through 4 except that fiber washers 127 are respectively employed between the surfaces 55 and and between the spring washer 71 and the surface 67. As the components of the centrifugal clutch assembly are otherwise generally of the same construction as that illustrated in FIGS. 2 through 4, the same reference numerals have been applied to the components shown in FIG. 7 as have been applied to the corresponding components in the con struction shown in FIGS. 2 through 4.

Various of the features of the invention are set forth in the following claims.

What is claimed is:

1. A centrifugal clutch assembly including a sprocket driver, a clutch drum supported for rotation independently of and co-axially with said sprocket driver and including a cylindrical surface adapted for releasable driving connection with a drive shaft in response to drive shaft rotation above a predetermined speed and a radially extending surface, and slip clutch means comprising said radially extending clutch drum surface, a cooperating surface extending radially on said sprocket driver in facing relation to said radially extending clutch drum surface, and means for holding said radially extending surfaces in frictional engagement with each other for torque transmission between said frictionally engaged radially extending surfaces only below a predetermined torque level.

2. A centrifugal clutch assembly in accordance with claim 1 and further including a chain sprocket mounted on and driven by said sprocket driver for common rotation therewith.

3. A centrifugal clutch assembly in accordance with claim 1 wherein said sprocket driver includes a shoulder formed by a cylindrical surface and by said radially extending surface and wherein said radially extending drum surface includes an aperture receiving therein said cylindrical surface of said sprocket driver.

4. A centrifugal clutch assembly in accordance with claim 1 wherein said clutch drum includes a portion de fined between said radially extending surface and a second surface spaced axially from said radially extending surface and wherein said holding means comprises a spring washer reacting between said axially spaced surface of said clutch drum and said sprocket driver.

5. A centrifugal clutch assembly in accordance with claim 4 wherein said sprocket driver also includes an annular groove adjacent to said surface and wherein said spring washer includes a portion located in said groove.

6. A centrifugal clutch assembly in accordance with claim 5 wherein said sprocket driver includes, in axially adjacent relation to said groove, a splined portion ineluding a series of ribs, and wherein said portion of said spring washer located in said groove includes pockets receiving the axially inner ends of said ribs, and further including a chain sprocket carried on said splined portion.

7. A chain saw comprising a frame, an engine supported by said frame, a rotatably mounted shaft driven by said engine, a centrifugal clutch carried on said shaft and including a clutch drum supported for rotation independently of and co-axially with said shaft and including a cylindrical surface, a radially extending surface, and means for releasably drivingly connecting said cylindrical surface with said shaft in response to shaft rotation above a predetermined speed so as to provide torque transmission between said shaft and said clutch drum in response to shaft rotation above the predetermined speed, a chain sprocket mounted for rotation co-axially with respect to said shaft, a sprocket driver rotatably mounted on said shaft and drivingly connected to said chain sprocket and including a surface extending radially in facing relationto said radially extending clutch drum surface, and means for holding said radially extending surfaces in frictional engagement with each other to afford torque transmission between said radially extending frictionally engaged surfaces only below a predetermined torque level.

8. A chain saw comprising a frame, an engine supported by said frame, a rotatably mounted shaft driven by said engine, a chain sprocket mounted for rotation co-axially with said shaft, a cutter bar supported by said frame, a saw chain trained around said sprocket and said cutter bar, and a centrifugal clutch assembly driven by said shaft and including a sprocket driver supported for rotation independently of and co-axially with said shaft and drivingly connected to said chain sprocket for common rotation therewith, a clutch drum supported for rotation independently of and co-axially with said shaft and including a cylindrical surface and a radially extending surface, means for releasably drivingly engaging said cylindrical surface with said shaft in response to shaft rotation above a predetermined speed so as to afford torque transmission in response to shaft rotation above the predetermined speed, slip clutch means for limiting torque transmission between said shaft and said sprocket driver and including said radially extending clutch drum surface and a cooperating surface extending radially on said] sprocket driver in facing relation to said radially extending clutch drum surface, and means for holding said radially extending surfaces in frictional engagement with each other for torque transmission therebetween only below a predetermined torque levels.

9. A chain saw in accordance with claim 8 wherein said sprocket driver includes a shoulder formed by a cylindrical surface and by said radially extending surface and wherein said radially extending drum surface includes an aperture receiving therein said cylindrical surface of said sprocket driver.

10. A chain saw in accordance with claim 8 wherein said clutch drum includes a portion defined between said radially extending surface and a second surface spaced from said radially extending surface axially of said shaft and wherein said holding means comprises a spring washer reacting between said axially spaced surface of said clutch drum and said sprocket driver.

11. A chain saw in accordance with claim 10 wherein said sprocket driver also includes an annular groove ading the axially inner ends of said ribs.

13. A chain saw in accordance with claim 8 wherein said chain sprocket is supported on said sprocket 

1. A centrifugal clutch assembly including a sprocket driver, a clutch drum supported for rotation independently of and coaxially with said sprocket driver and including a cylindrical surface adapted for releasable driving connection with a drive shaft in response to drive shaft rotation above a predetermined speed and a radially extending surface, and slip clutch means comprising said radially extending clutch drum surface, a cooperating surface extending radially on said sprocket driver in facing relation to said radially extending clutch drum surface, and means for holding said radially extending surfaces in frictional engagement with each other for torque transmission between said frictionally engaged radially extending surfaces only below a predetermined torque level.
 2. A centrifugal clutch assembly in accordance with claim 1 and further including a chain sprocket mounted on and driven by said sprocket driver for common rotation therewith.
 3. A centrifugal clutch assembly in accordance with claim 1 wherein said sprocket driver includes a shoulder formed by a cylindrical surface and by said radially extending surface and wherein said radially extending drum surface includes an aperture receiving therein said cylindrical surface of said sprocket driver.
 4. A centrifugal clutch assembly in accordance with claim 1 wherein said clutch drum includes a portion defined between said radially extending surface and a second surface spaced axially from said radially extending surface and wherein said holding means comprises a spring washer reacting between said axially spaced surface of said clutch drum and said sprocket driver.
 5. A centrifugal clutch assembly in accordance with claim 4 wherein said sprocket driver also includes an annular groove adjacent to said surface and wherein said spring washer includes a portion located in said groove.
 6. A centrifugal clutch assembly in accordance with claim 5 wherein said sprocket driver includes, in axially adjacent relation to said groove, a splined portion including a series of ribs, and wherein said portion of said spring washer located in said groove includes pockets receiving the axially inner ends of said ribs, and further including a chain sprocket carried on said splined portion.
 7. A chain saw comprising a frame, an engine supported by said frame, a rotatably mounted shaft driven by said engine, a centrifugal clutch carried on said shaft and including a clutch drum supported for rotation independently of and co-axially with said shaft anD including a cylindrical surface, a radially extending surface, and means for releasably drivingly connecting said cylindrical surface with said shaft in response to shaft rotation above a predetermined speed so as to provide torque transmission between said shaft and said clutch drum in response to shaft rotation above the predetermined speed, a chain sprocket mounted for rotation co-axially with respect to said shaft, a sprocket driver rotatably mounted on said shaft and drivingly connected to said chain sprocket and including a surface extending radially in facing relation to said radially extending clutch drum surface, and means for holding said radially extending surfaces in frictional engagement with each other to afford torque transmission between said radially extending frictionally engaged surfaces only below a predetermined torque level.
 8. A chain saw comprising a frame, an engine supported by said frame, a rotatably mounted shaft driven by said engine, a chain sprocket mounted for rotation co-axially with said shaft, a cutter bar supported by said frame, a saw chain trained around said sprocket and said cutter bar, and a centrifugal clutch assembly driven by said shaft and including a sprocket driver supported for rotation independently of and co-axially with said shaft and drivingly connected to said chain sprocket for common rotation therewith, a clutch drum supported for rotation independently of and co-axially with said shaft and including a cylindrical surface and a radially extending surface, means for releasably drivingly engaging said cylindrical surface with said shaft in response to shaft rotation above a predetermined speed so as to afford torque transmission in response to shaft rotation above the predetermined speed, slip clutch means for limiting torque transmission between said shaft and said sprocket driver and including said radially extending clutch drum surface and a cooperating surface extending radially on said sprocket driver in facing relation to said radially extending clutch drum surface, and means for holding said radially extending surfaces in frictional engagement with each other for torque transmission therebetween only below a predetermined torque level.
 9. A chain saw in accordance with claim 8 wherein said sprocket driver includes a shoulder formed by a cylindrical surface and by said radially extending surface and wherein said radially extending drum surface includes an aperture receiving therein said cylindrical surface of said sprocket driver.
 10. A chain saw in accordance with claim 8 wherein said clutch drum includes a portion defined between said radially extending surface and a second surface spaced from said radially extending surface axially of said shaft and wherein said holding means comprises a spring washer reacting between said axially spaced surface of said clutch drum and said sprocket driver.
 11. A chain saw in accordance with claim 10 wherein said sprocket driver also includes an annular groove adjacent to said surface and wherein said spring washer includes a portion located in said groove.
 12. A chain saw in accordance with claim 11 wherein said sprocket driver includes, in axially adjacent relation to said groove, a splined portion including a series of ribs, wherein said chain sprocket is carried on said splined portion, and wherein said portion of said spring washer located in said groove includes pockets receiving the axially inner ends of said ribs.
 13. A chain saw in accordance with claim 8 wherein said chain sprocket is supported on said sprocket driver. 